Processing valves within processing systems in the food, beverage and pharmaceutical industry as well as the fine chemical industry and biotechnology are incorporated in complex system controls. For this purpose, a valve control device is arranged on the processing valve and connected to the system controls. The valve control device reports the position of the processing valve to the system control and, in response to signals, changes the valve position once this is required by the process.
In earlier solutions, the position of the processing valve was determined by means of mechanical contacts. Microswitches and a component of the valve connected to a closing element touched each other. The component was designed to change the switching position of the microswitch by moving the component. The position of the closing element was determinable in this manner. Since this way of determining position was subject to wear, contact-free measuring methods were developed and successfully marketed.
Contact-free measuring methods are per se practically wear-free and possess the advantage of being able to perform a calibration when there is mechanical wear to valve parts, in particular the seal between the valve disk and valve seat. By means of this calibration, the closing position is also determined when, from the aging of the seal, it is reached in a changed position of the valve disc and valve seat relative to each other. Such a calibration method is described for example in WO 95/17624 A1 without further explanation of the contact-free measuring principle.
WO 02/093058 A1 presents both a calibration method as well as a device for the contact-free measurement of the valve position. A plurality of Hall sensors are used for measuring position that are arranged along the direction of movement of a permanent magnet connected to a valve rod moving one of the valve discs.
DE 10 2007 058 253 A1 explains another arrangement for contact-free measurement in a processing valve. A permanent magnet is affixed to the valve rod and interacts with a magnetorestrictive sensor.